Experiences from First Top-Off Injection At The Stanford ... · PDF fileInjection At The Stanford Synchrotron Radiation Lightsource Johannes Bauer, ... – Connected with BTS line

Experiences from First Top-Off Injection At The Stanford

Synchrotron Radiation Lightsource

Johannes Bauer, James Liu, Alyssa Prinz, Sayed Rokni

Radiation Protection Department

SLAC National Accelerator Laboratory

Menlo Park, CA 94025, U.S.A.

RADSYNCH’09

Trieste, Italy

May 22, 2009

J.M.Bauer, “SSRL Top-Off Experiences”

RADSYNCH’09, May 22 2009, Page 2

Overview

• Introduction to SSRL

• Introduction to “Top-Off”

• Studies in Preparation for Top-Off

• Safety System

• First Tests

• SSRL Improvements

• New Tests

• Conclusions and Path Forward



Introduction to SSRL

“Stanford Synchrotron Radiation Lightsource”

• Evolved from high-energy physics synchrotron “SPEAR”

• Twice upgraded, now:

– Storage ring SPEAR3

– Fed by 10 Hz Linac (to 150 MeV), Booster (to 3 GeV)

– Connected with BTS line (Booster-To-SPEAR)

• 3 GeV, 100 mA with typically 1 W injectionusually three times a day fill from ~85 mA to 100 mA

• Going to 500 mA this year, later up to 5 W injection

• Currently 13 beamlines with 27 stations



Introduction to SSRL (cont.)



Introduction to SSRL (cont.)

SPEAR3

BTS(Booster-to-SPEAR)

Linac &

BoosterBeamlines



So far: Injection stoppers (IS) closed while filling storage ring

no worries about electrons and Bremsstrahlung reaching BL

during injection

but temperature changes (alignment) affect optical components:

o.k. now, but not desired at higher currents

Top-Off: Filling storage ring while injection stoppers open

– “Infrequent injection”: 3+ times a day

– “Trickle injection”: up to once every minute

injector stays on, must stay tuned, high instantaneous charge

At other facilities “top-off” called “top-up”

Top-off, Top-Up, etc.

impractical unless IS stay open



Top-off, Top-Up, etc. (cont.)

Q = 5 A hr: Higher beam currents shorter lifetime higher losses

infrequent injection

trickle injection



SSRL Ray Trace Studies

Beam chamber apertures and magnets constrain

where beam can go

Studies by SSRL (with LBNL) to answer:

• How far towards beamline can injected beam travel with

which magnet settings?

• Which magnet settings prevent beam from going past safe

endpoints?

Safety Systems designed to keep beam within safe endpoints



QF QD BEND SDINSERTION DEVICE

A1 A2

Stored Beam on

design orbit

Ratchet

Wall

Fixed

Mask I

Fixed

Mask II

Comb

Mask

CM

Section of SPEAR BeamlineIncoming Beam

Assume all positions

and angles are

possible

No distinction between

stored beam, injected

beam on the 1st turn,

and injected on

subsequent turns

Energy error

No magnetic field

Straight line trajectories

Beamline Apertures

Vacuum Chamber

Radiation Masks

Magnetic field in all elements

ID – insertion device + trim coils

BEND – dipole magnet

QF – focusing quadrupole

QD – defocusing quadrupole

CM – horiz. corrector magnet

SD – defocusing sextupole

SPEAR Apertures

Vacuum Chamber

Radiation Masks

Safe

Endpoint

Start

Point

Region for trajectory simulations

Thanks to A.Terebilo, SSRL

SSRL Ray Trace Studies (cont.)



Radiological Considerations

(1) Long-term dose from normal operation:Additional radiation from:

– forward-angle Bremsstrahlung from injected beam at apertures– higher beam currents

Based on estimated loss rates: within 1 mSv (100 mrem) per 1000 hr limit

(2) Radiation dose due to mis-steered beamWithin bounds of safety systems,

but such serious mis-steering expected only very rarely

Safety system defines “safety endpoint” that electrons cannot pass

Simulations up to 22 mSv/h (2.2 rem/h at 5 W) for dipole lines, ~20% less for ID lines – always radiation monitors in place

(3) Radiation due mis-steering with full safety system failureShould never happen; VERY UNLIKELY; requires several serious failures

Simulations dose rate high, up to 3.3 Sv/h (330 rem/h) at 5 W for dipole lines, up to 0.13 Sv/h (13 rem/h) for ID lines

but per event (<1 s) 0.74 mSv (74 mrem) with radiation monitors in place



Top-Off Safety Systems

Beam Containment System (BCS):

• Stored Current Interlock: top-off only for >50 mA

• Apertures: may not be modified without approval

• Magnet Power Supply Interlocks: monitoring both current and voltage

• Clearing Magnets: along dipole beamlines (no space for permanent magnets)

• Dose Rate Interlock: radiation monitors tripping at 0.02 mSv/h (2 mrem/h)

Non-BCS Systems:

• Daily Dose Interlock: rad. monitors allow max. 0.01 mSv (1 mrem) per day

• Charge Loss Interlock: allow only certain # e- lost each day

• Additional: Machine protection interlocks and software warnings (tight limits)



• April to July 2008

• Interlocked BSOICs next to hutch

• Floor cleared, most data read out remotely:

– Beam Shut-Off Ion Chambers (BSOIC) SLAC-built

– Beamline Radiation Monitors HPI 6030/6012

• Access restricted:– No access during tuning

– Electronic “chirping” dosimeters

– Handheld dose meters

First Tests



• High-efficiency injection

(1 W injection, ~60-80% injection efficiency)

• Low-efficiency injection due to BTS mis-tuning

(1 W, ~30-50% injection efficiency)

Losses inside SPEAR ring at apertures

• Zero-efficiency injection

(1 W, 0% injection efficiency)

All of injected beam lost in ring due to “bump” at beamline

(orbit moved towards edge of aperture)

Beam Conditions for Tests

similar results



Measurements with Old Injection

BL55 microSv/h

(0.5 mrem/h)

already at

high-efficiency

injection

high-efficiency inj. < --- > low-efficiency inj.

BL11radiation only

at inefficient

injection

injection

current

throughout

0.16 0.04 nA

11 microSv/h

(1.1 mrem/h)

7 microSv/h

(0.7 mrem/h)



Measurements with Old Inj. (cont.)

Three “types” of beamlines were found:

1. BL 4, 5:

Extra radiation seen during both

high-efficiency injection, up to 18.5 microSv/h (1.85 mrem/h)

and low-efficiency injection, up to 30 microSv/h (3 mrem/h)

2. BL 10, 11:

No extra radiation seen during high-efficiency injection,

but during low-efficiency injection, up to 16 microSv/h (1.6 mrem/h)

3. BL 1, 2, 6, 7, 9:

No or very little, < 1 microSv/h (< 0.1 mrem/h), extra radiation

seen during high- or low-efficiency injection

BL 8, 12, 13, 14: Ray trace studies not yet approved; BLs not tested



Dose Extrapolations - Old Injection

• No issues for any

BL at 100 mA

top-off operation

BL100 mA Infrequent Total dose

microSv/1000h mrem/1000h

BL 1 0 0

BL 2 4 0.4

BL 4 110 11

BL 5 190 19

BL 6 14 1.4

BL 7 10 1

BL 8 Ray trace study not yet approved, BL not tested

BL 9 3 0.3

BL 10 80 8

BL 11 80 8



Extrapolations

based on

measurements &

operation scenarios



Dose Components

Radiation from stored beam (s), injected beam (i),

traveling through wall (w), through beam pipe (b)

Dsb

Dib

DiwDswTerm unique for

top-off injection

Injection Stoppers



Dose Extrapolations - Old Injection

Dose components at 500 mA trickle injection

in mSv/1000h and mrem/1000h

BL Dib Diw Dsb Dsw Total

BL 1 0 0 0 0 0 0 0.01 1 0.01 1

BL 2 0 0 0 0 0 0 0.1 10 0.10 10

BL 4 0.93 93 0.02 2 1.32 132 0.06 6 2.33 233

BL 5 2.34 234 0.14 14 1.07 107 0.06 6 3.62 362

BL 6 0.05 5 0.05 5 0.18 18 0.02 2 0.30 30

BL 7 0.05 5 0 0 0 0 0.18 18 0.23 23


BL 9 0 0 0 0 0.08 8 0 0 0.08 8

BL 10 0.94 94 0.01 1 0.32 32 0 0 1.27 127

BL 11 0.15 15 0.04 4 1.66 166 0.08 8 1.93 193



Dose components at

500 mA trickle injection

Dib high for BL 4, 5, 10

Dsb high for BL 4, 5, 11

lower with

new injection

Stored beam dose

measured with

GM/BF3 detector

Requires additional

shielding for higher

currents



SSRL Improvements to Injection

Injection system was adequate up to now;

top-off raised the bar, and SSRL responded

• Studied changes in x, y, x’, y’, energy, timing, optics

of injected beam

• New diagnostics added

• Better control of trajectory and optics

(computer monitoring, frequent checks)

• Removal of windows in BTS line:

Now one vacuum system from Linac to SPEAR



SSRL Improvements to Injection (cont.)

• Simulations show big improvement

very clear in y and y’ distributions of injected beam

injection efficiency83% 99% in simulation

• Similar simulation for optics

• Measured radiation doses went down

Thanks to J.Safranek, X.Huang, SSRL

with windows removed

windows present



• Repeat with improved injected beam (fall 2008)

• Measurements during high-efficiency injection

BL 4: 1.2 microSv/h 0.12 mrem/h

BL 5: 1.6 microSv/h 0.16 mrem/h

BL 10,11: 0 microSv/h 0 mrem/h

Dose rates about 10 times lower than before!

Worst 1.6 microSv/h (0.16 mrem/h) extrapolated to 1000 hour/year:

Dib = 5 microSv (0.5 mrem) for 100 mA infrequent injection56 microSv (5.6 mrem) for 500 mA infrequent injection92 microSv (9.2 mrem) for 500 mA trickle injection

(was 2.34 mSv or 234 mrem before)

Measurements with New Injection

The four worst BLs before!



Dose Extrapolations - New Injection

Dose components at 500 mA trickle injection

in mSv/1000h and mrem/1000h

BL Dib Diw Dsb Dsw Total

BL 1

BL 2

BL 4 0.07 7 0.02 2 1.32 132 0.06 6 1.47 147

BL 5 0.09 9 0.14 14 1.07 107 0.06 6 1.36 136

BL 6

BL 7


BL 9

BL 10 0 0 0.01 1 0.32 32 0 0 0.33 33

BL 11 0 0 0.04 4 1.66 166 0.08 8 1.78 178



Dose components

at 500 mA trickle

injection

Dib now low!

No effects on Dsb

(to be improved by

shielding; reduction to

1/10 for higher current

operation)



• Injection with low efficiency

BL4: 1.2 microSv/h 0.12 mrem/h




Again lower dose rates than before

Worst 4.8 microSv/h extrapolated to 1000 hour/year

Dib = 2.8 mSv (280 mrem) at 500 mA trickle injection

(50 min to reach 100 mA)

Measurements with New Inj. (cont.)



Summary of Test & Path Forward

• Tests taught us:– Improved injection well enough even for 500 mA trickle injection

– No long-term dose rate concerns for 100 mA (June 2009)

• More beamlines will be added over time

• For top-off up to 200 mA (July 2009)

– Warning system for injection beam lattice and optics

– Daily Dose Interlock

– Charge Loss Interlock

• For > 200 mA (stored beam issue) (Fall 2009)

– Additional shielding for BL4, 5 and 11

– Mitigation systems for BL thermal damage issues

• Review for trickle charge injection (beyond 2009)& injector upgrade (>1.5 W)



Conclusions

• Tests very interesting: higher dose rates measured than expected

• SSRL was able to improve injection system

• With improvements top-off o.k. even for 500 mA trickle injection

• Stored-current dose needs to be addressed for >200 mA

• Top-off will start soon, later going to higher currents

Documents

Experiences from First Top-Off Injection At The Stanford ... · PDF fileInjection At The Stanford Synchrotron Radiation Lightsource Johannes Bauer, ... – Connected with BTS line